Source : Webster's Revised Unabridged Dictionary (1913)

Annotation \An`no*ta"tion\, n. [L. annotatio: cf. F.
   annotation.]
   A note, added by way of comment, or explanation; -- usually
   in the plural; as, annotations on ancient authors, or on a
   word or a passage.

Source : WordNet®

annotation
     n 1: a comment or instruction (usually added); "his notes were
          appended at the end of the article"; "he added a short
          notation to the address on the envelope" [syn: {note}, {notation}]
     2: the act of adding notes [syn: {annotating}]

Source : Free On-Line Dictionary of Computing

annotation
     
        1.  Extra information associated with a
        particular point in a document or program.  Annotations may be
        added either by a {compiler} or by the programmer.  They are
        not usually essential to the correct function of the program
        but give hints to improve performance.
     
        2.  A new commentary {node} linked to an existing
        node.  If readers, as well as authors, can annotate nodes,
        then they can immediately provide feedback if the information
        is misleading, out of date or plain wrong.
     
        (1995-11-26)